356 THE SNAKES OF SOUTH AFRICA. 
blood to escape through the walls of the blood vessels into the 
surrounding tissues. The phagosytes are the white corpuscles 
of the blood. They are altered, damaged, and often more or less 
dissolved by the action of the hemorrhagin principle in snake 
venom. The chief action, however, is upon the red corpuscles 
of the blood. The hemorrhagin attacks these corpuscles, dis- 
solving out their colouring matter and rendering them spherical 
and sticky. This dissolved colouring matter then escapes 
through the expanded walls of the blood vessels and finds its 
way into the tissues, spreading out under the skin and causing 
purple blotches more or less extensive. This escape of blood 
into the tissues is greatest near the various small arteries which 
branch off and terminate in a fine network of capillaries. The 
reason is that, at these points, the pressure of blood upon the 
capillaries is greatest. 
The broken-up blood also oozes out through the mucous or 
lining membranes of the mouth, nose, lungs, stomach, bowels, 
and bladder. This blood-destroying poison predominates in 
Adder venom. Recent experiments, however, tend to show that 
the venom of the Puff Adder acts chiefly if not entirely on the 
endothelial cells, and not on the blood corpuscles. 
(3) FIBRIN-FERMENTS. These cause the fibrin of the blood 
to solidify, which produces clotting. These fibrin ferments are 
usually strongest in Viper venoms, although they are present in 
lesser or greater degree in the poisons of all snakes. 
When human subjects are bitten by Vipers (Adders) this 
fibrin-ferment does not cause coagulation of the blood, unless 
injected in an unusually large quantity, or direct into a vein 
(intravenously). In the latter cases, coagulation of the blood and 
death may occur at any instant. When injected direct into a 
vein even in small quantity death occurs within a few moments. 
However, when the small animals on which snakes feed, such 
as rats, mice, or birds, are bitten by Adders, the fibrin-ferment 
in the venom almost instantly coagulates their blood, causing 
rapid death. This is due to the relatively large dose of venom 
injected. In the case of man or the larger mammals, sufficient 
of the fibrin-ferment principle in the venom does not usually 
enter the blood all at once to cause clotting, as is usual with small 
creatures. In the case of Cobras, the neurotoxin or nerve poison 
is the principal factor in causing the rapid death of their prey. 
